ABSTRACT All living organisms require exogenous foods/nutrients for producing energy in the form of Adenosine Triphosphate (ATP), which is needed for numerous cellular functions and is efficiently produced in mitochondria that are intimately involved in the generation of and defense against reactive oxygen species (ROS). An early event that occurs in response to alcohol consumption is mitochondrial dysfunction, which is evident in changes to the mitochondrial proteome, respiration defects and mitochondrial DNA (mtDNA) damage. These effects of ethanol are prominent in the liver, the major site of ethanol metabolism in the body, promoting both apoptotic and necrotic cell death and contribute to the onset or progression of alcohol-induced liver diseases (ALD), leading to hepatic fibrosis/cirrhosis and cancer. SUMOylation is a posttranslational modification that involves addition of SUMOs (small ubiquitin-like modifiers) modulating protein stability, activity and localization. Several studies have intimated a close relationship between SUMOylation and ROS. We recently demonstrated that Ubiquitin Conjugating Enzyme 9 (UBC9), the sole E2 protein required by SUMOylation machinery, is upregulated in Intragastric fed-mice liver (IE) and cirrhotic tissues. We also found that UBC9 is phosphorylated and this is correlated with high level of SUMOylation activity in lipopolysaccharides-activated Kupffer cells that leads to inflammation development. In addition, we elucidated the key function of SUMOylated microsomal Cytochrome P450 2E1 (CYP2E1) in ALD that sustains its enzymatic activity and protein stability. Much of the detailed investigation of the role of SUMOylation in ALD has been started in our laboratory. However, several important mechanistic pathways that are altered in ALD have not been investigated yet. In order to explore the role of SUMOylation in ALD, Mass Spectrometry (MS) was performed to identify SUMOylated proteins in 10-day ethanol-feeding+1 Binge ethanol (NIAAA) model, where SUMOs binding columns were used to purify SUMOylated proteins from total livers. Interestingly, we found that ethanol induces changes in SUMOylation state of several mitochondrial proteins involved in ATP synthesis (ATP5B, SOD2, CLC25A5, HSPD1, FBP1, CYCS), ATP metabolism (ATP5A1, ATP5B, ATP5C1, ATP5F1, ATP5J2, ASPA8, AK3), and mitochondria disorder (UQCRC2, PC, HMGCS2, ECHS1, COX6B1, NDUFV3, COX6C). These finding could suggest a potential role of SUMOylation in oxidative phosphorylation, electron transport chain (ETC) and respiratory control ratio may be modulating the ability of these proteins to form the complex above and/or regulating their activity. This proposal tests the novel hypothesis that ethanol induces mitochondrial dysfunction in ALD regulating the SUMOylation status of key respiratory chain proteins and explore the molecular mechanisms. Two specific aims are proposed: 1) Explore the role of SUMOylation in ethanol-modulated ETC and ATP production, 2) Examine the role of SUMOylation in ethanol-induced CYP2E1 for maintenance of mitochondrial oxygen homeostasis. If successfully completed, these studies should provide highly novel information on the role of SUMOylation in the development of ALD and may provide novel therapeutic strategies, which is of high